You'll hear all sorts of wild claims but the native EI rating of the Z1 camera is about 100 EI (as advised by Sony). You can get more out of it on an interior set up but grain becomes a factor. Depending on how much grain you mind, you can get more out of it that that. When set up properly on a macbeth chart for exposure I was able ot bracket it at ?2 stops under exposure to +2.5 over exposure as a safe range of under/over without compromising picture. Outside of that, depending on factors such as lenses, gain settings, and subjective taste, you can successfully rate the camera up to 800. But for true blacks and a grainless picture 100 is the baseline. Then again it depends on where your final product is going to. You can get away with much more on a Tv screen. If you are doing a filmout, you are lmiited, etc.

Problem is that the exposure index of a video camera is not a perfectly skiable MTF slope as it is with film so the answer to the question has to do with how much llight you are talking. Exterior will give you a different exposure index (ASA is not a correct term to use in video language although everyone does) than you will get in an interior. But then again to make sure you are getting at least 75% MTF outdoors you want to use the ND filter in camera and if necessary additional add-on ND filters to keep your lens wider than 5.6 or else you throw away resolution.